When semiconductor chips are to be mounted on substrates or interposers to form today's semiconductor packages, the substrates and interposers are commonly made of plastic or ceramic materials. These materials are especially preferred when the chip assembly technique employs the flip-chip method using solder balls to create the electrical connections between the chips and the substrate/interposer. When the assembled devices are then used or tested under conditions, which impose wide swings of temperature or humidity on the packages, significant failure rates may appear, characterized by cracks, especially at the solder joints, and delamination of the package parts.
Driven by the desire to reduce the board area needed to assemble a semiconductor device into electronic products such as hand-held telephones, today's semiconductor devices often use vertically stacked chips inside the packages. These chip stacks frequently include chips of significantly different sizes, assembled mostly by wire bonding techniques on interposers made of plastic or ceramic materials. The stack on the interposer is then assembled on substrates with solder balls for interconnection to external parts. The reliability failure rates due to solder joint cracks or parts delamination, observed for these devices under conditions of temperature cycles and high humidity, are especially high.
In order to interface an integrated circuit with other circuitry, it is common to mount it on a lead frame or substrate. Each integrated circuit has bonding pads that are individually connected to the lead frame's lead finger pads using extremely fine gold or aluminum wires. The assemblies are then packaged by individually encapsulating them in molded plastic or ceramic bodies to create an integrated circuit package.
Integrated circuit packaging technology has seen an increase in the number of integrated circuits mounted on a single circuit board or substrate. The new packaging designs are more compact in form factors, such as the physical size and shape of an integrated circuit, and providing a significant increase in overall integrated circuit density. However, integrated circuit density continues to be limited by the “real estate” available for mounting individual integrated circuits on a substrate. Even larger form factor systems, such as PC's, compute servers, and storage servers, need more integrated circuits in the same or smaller “real estate”. Particularly acute, the needs for portable personal electronics, such as cell phones, digital cameras, music players, PDA's, and location-based devices, have further driven the need for integrated circuit density.
This increased integrated circuit density, has led to the development of multi-chip packages in which more than one integrated circuit can be packaged. Each package provides mechanical support for the individual integrated circuits and one or more layers of interconnect lines that enable the integrated circuits to be connected electrically to surrounding circuitry. Current multi-chip packages, also commonly referred to as multi-chip modules, typically consist of a PCB substrate onto which a set of separate integrated circuit components is directly attached. Such multi-chip packages have been found to increase integrated circuit density and miniaturization, improve signal propagation speed, reduce overall integrated circuit size and weight, improve performance, and lower costs—all primary goals of the computer industry.
Multi-chip packages whether vertically or horizontally arranged, can also present problems because they usually must be pre-assembled before the integrated circuit and integrated circuit connections can be tested. Thus, when integrated circuits are mounted and connected in a multi-chip module, individual integrated circuits and connections cannot be tested individually, and it is not possible to identify known-good-die (“KGD”) before being assembled into larger circuits. Consequently, conventional multi-chip packages lead to assembly process yield problems. This fabrication process, which does not identify KGD, is therefore less reliable and more prone to assembly defects.
Moreover, vertically stacked integrated circuits in typical multi-chip packages can present problems beyond those of horizontally arranged integrated circuit packages, further complicating the manufacturing process. It is more difficult to test and thus determine the actual failure mode of the individual integrated circuits. Moreover the substrate and integrated circuit are often damaged during assembly or testing, complicating the manufacturing process and increasing costs. The vertically stacked integrated circuit problems can be greater than the benefits.
There are design limitations presented by package stacks as well. In many of the stacked structures, the top package is not able to have system interconnects in the center as this area is usually consumed by the plastic package cover of the lower device. In the push for more integrated function, this limitation may stop a design from using the package type. Package overlaps have long been a barrier to additional interconnects, which can be a problem in a device that has a high number of interconnects around the outside of the package.
Thus, a need still remains for an integrated circuit packaging system with package-on-package stacking that can provide smaller and reliable packages with high yields. In view of the shrinking size of consumer electronics and the demand for more sophisticated functions in the restricted space, it is increasingly critical that answers be found to these problems. In view of the ever increasing commercial competitive pressures, increasing consumer expectations, and diminishing opportunities for meaningful product differentiation in the marketplace, it is increasingly critical that answers be found to these problems. Moreover, the ever-increasing need to save costs, improve efficiencies, and meet such competitive pressures adds even greater urgency to the critical necessity that answers be found to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.